The present invention relates in general to water heater construction and more specifically, to the design of the outer shell for commercial and residential water heaters.
The majority of conventional commercial and residential water heaters are fabricated with an inner storage tank and an outer shell. A designed clearance space between these two generally concentric members is provided for the receipt of a suitable insulation. The outer shell is typically a singular cylindrical member which must be assembled over the tank by closely and carefully aligned axial movement of either the tank or the shell relative to the other.
One difficulty with this assembly technique is the time required due to the fact that with insulation disposed around the inner tank and a desire to compress that insulation slightly, great care must be taken with this axial sliding operating. Another concern, though related to the foregoing, is how to maximize the amount and coverage of insulation. Clearly, by increasing the thickness of insulation heat transfer losses from the tank are minimized thus reducing energy costs attributable to heating the water within the tank. However, if the thickness of insulation is too great, it will not be possible to slide the outer shell down over this insulation without significant problems of pulling and tearing the insulation to the point that the finished product is unacceptable and the insulation must be replaced and the assembly procedure repeated.
Some of the specifics as to the design of the insulation will depend upon the type of insulation used. Different design parameters exist depending upon whether the annular space between the tank and the shell is to be filled with foam insulation or an insulation blanket or both. For example, my prior, issued patents, U.S. Pat. Nos. 4,736,509 and 4,744,488 relate generally to design concepts and water heater construction concepts.
As mentioned, the annular space between the tank and the shell may also be filled by means of an insulation blanket which is draped over the tank prior to lowering the shell in place. For improved results, it is helpful to compress the insulation blanket. However, since there are difficulties in assembling the shell in a manner to achieve compression without pulling or tearing the blanket, the result is to use a relatively thin blanket of insulation so as to permit the assembly of the outer shell. Nevertheless, even with a relatively thin blanket there is some pulling and a risk of tearing and thus with insulating material such as fiberglass, it is difficult if not impossible to achieve 100% coverage.
A further option as to the insulation concept is to use a combination of a partial blanket or insulation dam or barrier and foam-in-place insulation disposed above the upper edge of the blanket or dam. My prior, co-pending applications, Ser. Nos. 177,392, 177,393 now U.S. Pat. No. 4,844,049 and 216,384 are examples of this combination insulation structure.
As various insulation concepts and construction concepts are evaluated, the speed and ease of assembly are important consideration. The appearance of the finished product is also important since attractive designs are a factor in purchasing decisions, possibly as one indicator of product quality. Since water heaters are typically mass-produced, there is a fast moving assembly line in the more efficient operations. Any design of tank, shell and insulation must keep the pace of the assembly line in mind.
Concepts and structures employed by others in the design and insulation of water heaters include the use of a bag to receive foam insulation. In one arrangement, when used with electric water heaters, the bag does not extend the full 360 degrees of the tank's circumference. Openings are left for the electrical controls. One concern with this insulation concept is the ability to get even distribution of the foam throughout the bag so that the finished product is very similar to an insulation blanket as to its uniformity and thickness. In this particular design the bag can be installed and then foamed after assembly of the shell, though again, complete coverage is a hit or miss proposition. In another arrangement, the bag may be pre-foamed and then assembled. The assembly time is though excessive with this approach and the bag even in this instance does not always foam evenly or completely thus leaving voids for heat loss leaks.
One example of the foregoing bag concept is illustrated in U.S. Pat. No. 4,527,543 which issued July 9, 1985 to Denton. In this structure a plastic envelope is wrapped entirely around the tank, or part of the tank if it is an electric water heater. After the outer shell is assembled, a foam-type insulation material (in liquid form) is injected into the envelope. A vent hole in the top cover provides an air vent during the foaming operation and also serves to provide a visual indicator for determining when the envelope is filled. Another patent to Denton, U.S. Pat. No. 4,447,377 which issued May 8, 1984, discloses a similar structure and insulation concept.
In U.S. Pat. No. 4,749,532 issued June 7, 1988 to Pfeffer there is disclosed yet another insulation concept. In Pfeffer a band of insulation is cinched to the tank such that the top and bottom edges flare outwardly beyond the location of the shell wall. In order to install the shell without tearing or pulling, a "shoe horn" type device is used to compress the outer edges inwardly as the shell is lowered into place. Thereafter the shoe horn is removed.
Although there are yet other designs where the insulation is wrapped around the tank, in each such configuration the outer shell is a singular, cylindrical member which must be assembled by axial sliding motion relative to the tank. Example of wrap-around insulation can be found in U.S. Pat No. 4,282,279 issued August 4, 1981 to Strickland and U.S. Pat. No. 4,039,098 issued August 2, 1977 to Stilts. In Strickland ('279), while the art is different and possibly unrelated to the present invention, there is disclosed an insulation blanket which is designed to be wrapped around a cylindrical tank (beverage can) and the free ends are thereafter secured together. In Stilts ('098), a thermal insulation jacket is provided where the free ends are joined by strips of tape.
In the present invention, the singular, cylindrical outer shell is replaced with a split generally cylindrical, wrap-around shell which may be opened and closed in a hinged movement so that the axial sliding procedure of prior shell designs can be eliminated. The construction of the present invention solves many of the current problems and provides an ease and efficiency of fabrication which is not presently available. The problems as to the integrity and completeness of the insulation which is disposed between the inner tank and the outer shell do not exist and the integrity and completeness can be confirmed before the shell is closed in place around the insulation.
The present invention contemplates an initially flat, though flexible, shell which is formed into two generally semi-cylindrical portions which are joined along one edge in a hinged fashion and the opposite free ends are secured together at the completion of the closing operation. A number of configurations are available for the hinge mechanism as well as for securing the free ends together. An alternative is simply to provide enough flexibility in the shell material that hinging-type movement can occur without using an actual hinge. A review of the cited references reveals that prior designs have never envisioned such a shell design, even in view of the many advantages and improvements which the present invention offers. It was not until the conception of the present invention that this idea came into being.